Will audio gear be ok in unheated house

Beginning to sound like it's just easier to take your speakers with you!

Peace of mind knowing they're safe.

In the long run, leaving your stereo equipment in an unheated home where the outside temperature drops below freezing and/or below 50 degrees where dampness exists, is not a good idea, and eventually will damage your equipment.

Fwiw, I've left my porch system (Integra receiver and disc changer) outside in a cabinet through ten Chicago winters and it still works fine. Now, I wouldn't be so cavalier with high-end gear, and I don't recommend it for others, but there you go.

I don’t think any of that equipment will be damaged in any way. I’ve left some good quality equipment in an I heated storage unit w/ no issues at all; speakers, turntable, electronics. It’s rapid changes in temperature that can be harmful, not slow steady ones within the temperature range your house will experience. 
 

As previously mentioned, by far the most potentially damaging thing you can do is turning on equipment while it’s still very cold.  Any moisture that might be present can get quickly heated by some components like resistors, transformers etc & then condense on a nearby cooler component & then short out. 

I experienced this first hand many years ago when I turned on a TV that was out in the garage on winter & a small fireworks show ensued. Lesson learned on a fortunately a piece of junk. Lesson learned. 
 

I own and rent cottages in one of the most inhospitable temperature-wise places in the US. Temps regularly hit -20F in the winter.

I also own a house (that I occupy) on the property.

I have left lots of equipment out in the barn over the winter. Obviously not my high-end stuff, but lots of CD players, extra preamps, as well as TVs, spare electronics for both the main house, as well as the cottages.

I've also owned boats which had lots of expensive electronic equipment in them (radar, GPS, radios, depthfinders, etc...).

All have been fine over the winters, just let them acclimate before turning them on.

Do NOT put your stuff in a closed closet with a space-heater and leave it unattended. The light-bulb thing (incandescent) is fine (I used to do it in the bilge of my boats, mostly to keep the bilge pumps from feezing up), but that's only going to do so much if the temps REALLY drop.

You state you've been leaving your speakers over-winter there, so no need to worry about the finish on them (cracking veneer, or what-have-you).

I have lots of direct experience with this very subject. Take my word for it, you'll be fine. Manufacturers ship their equipment sealed in plastic bags with silica gel packets as a desiccant. That equipment usually crosses the ocean on a freighter or in the unheated cargo hold of an airplane.

You'll be fine.